This invention relates to digital graphics, and more particularly to a method and apparatus for digital image object tracking and segmentation.
In composing and manipulating digital images for providing special effects in movie and video clips and for a variety of other imaging and graphics applications, image objects are identified and tracked. In movies, for example, image objects are inserted or manipulated to alter a scene in a realistic manner. Objects or regions from still frames or photographs are inserted into a sequence of frames to create a realistic image sequence.
Segmentation is a technique in which an object within an image is traced so that it may be extracted. Among the earliest segmentation methods is a manual method in which an operator manually selects points along a boundary of the object to outline the image. The points then are connected to formed a closed object. For example, straight lines have been used to connect the points. The more points selected the more accurate the outline.
An active contour based segmentation process improves on the manually selected rough approximation using an edge energy function. The edge energy function is computed based on a combination of internal forces relating to curve energy and external forces related to image gradient magnitude. The active contour minimizes the edge energy function to approximate the object boundary in an iterative process.
One shortcoming of edge based tracking and segmentation methods is the difficulty in identifying video objects or object portions with a rapidly changing shape. For example tracking a human leg during a scene where the person is walking is difficult because the shape of the leg is continually changing. Difficulties also arise in tracking objects or object portions which are being occluded and disoccluded in various image frames. Accordingly, an alternative approach to object tracking is desired which is able to track rapidly moving objects and objects which are being occluded and disoccluded in various frames.